1. Field of the Invention
The invention concerns triggering a change of state of a scanner mechanism from an idle or non-scanning state to an active scanning state, upon detecting movement of a resilient element provided in the scanning mechanism. In one embodiment, the movable element is the resonating flipper element that carries a reflector for scanning the beam, being driven in a feedback loop by an oscillator that is gated off during periods of inactivity. At least one mode for switching from the idle state to the active scanning state comprises setting a latch from an output of a feedback amplifier in the driving circuit. In addition to latching-on from detection of a minor shock or vibration so as to switch into the active state, the circuit is useful to verify that movement has commenced when switching into the active state via a different mode.
2. Prior Art
Bar code readers and similar beam scanning devices are used in various environments such as capturing product identification codes at retail point-of-sale stations, inventory and document tracking, order assembly and shipping and receiving, and in various other automatic data capture situations. An illuminating beam typically is scanned repeatedly over the code, using one or more reflectors that are moved so as to direct the beam from a fixed laser diode or the like along a scanning path. In a configuration exemplified in U.S. Pat. No. 6,227,450—Blake et al. (which is hereby incorporated in this disclosure), a flexible resilient polymer strip is fixed to a housing at one end, has a reflector on a side of the strip, and carries a magnet spaced from the fixed end. The magnet is subjected to electromagnetic force by an oscillator coupled to a coil that causes the strip to oscillate back and forth, thus tilting the reflector back and forth and directing the beam repetitively back and forth along a scan line.
Such a scanner may be mounted in or on a countertop or adjacent to a conveyor. To facilitate directing the scanning beam over the bar code, the scanner may comprise a movable scanning head that the user aims at the bar code. The scanning head may be tethered by a cable for managing power and communications lines, or may be self contained, battery powered and arranged for uploading data from time to time.
Battery powered hand-held scanners may be arranged to connect to a power and data communications connection (such as a USB port) or to dock in a stand at which the battery of the hand-held scanner can be charged. The device is not typically used in for scanning when in the stand, and power consumption and battery life are product design issues. To maximize battery life, hand-held scanners often have three distinct modes, namely “on,” “off” and a standby or “sleep” mode. In the sleep mode, some circuit sections are at least partly disabled or unpowered, including the oscillator that electromechanically powers the scanner. A scanner may be configured automatically to enter the sleep mode if a predetermined time period elapses without scanning a readable bar code.
When the scanner is in sleep mode, arrangements are provided in response to some signal or switch closure or sensed event to reactivate or “wake-up” the scanner as needed to resume regular operation. Several of methods for waking scanners and similar devices are known in the art. One method of activating a quiescent scanner involves changing the state of a switch or trigger mechanism on a scanner head that a human user grasps, lifts from a dock or cradle or otherwise moves when commencing to aim the scanning head at a bar code to be read. The trigger mechanism may comprise a touch plate coupled to a circuit responsive to a change of capacitance that occurs when a human touches the device. A mechanically operated conductive trigger switch may be included that must be depressed or released or toggled. Other possibilities include tilt or weight responsive switches for a standing unit, magnetic or inductive couplings with a docking base, etc. Wake up switches and interlocks as described are not wholly satisfactory because they add expense and complication.
One method of triggering a change from quiescent to active operation is to detect that the scanning head has been redirected, potentially to be aimed, or that an item has been brought in front of the scanner, presumably to be scanned. For these objects, an infrared (IR) detector can be used to generate an activation triggering signal when the subjects in the field of view move relative to the detector. This technique is functionally apt because attempting a scan generally involves changing the position of the scanner relative to an item to be scanned or relative to fixed background items.
However, an IR source and detection circuits carry an associated expense in terms of parts, maintenance and power dissipation overhead. The power drain is particularly heavy because it is necessary to emit and detect IR signals throughout the period in which the scanner is quiescent in order to detect a movement of subjects in front of the scanner when it finally occurs. This technique is generally unsuitable if the scanner is to run on battery power.
Another known method of waking a scanner comprises intermittently activating the scanner according to a timer, at least to the extent necessary to determine from a test or partial scan that a bar code may be present (e.g., to detect contrasting brightness along a line in the field of view). In this method, the scanning assembly (e.g., the light source, oscillating mirror assembly and accompanying electrical circuitry) is activated momentarily at a predetermined schedule. The time interval between attempts needs to be relatively short because otherwise a user who wants to scan an item might be required to wait an undue time for the scanner to activate. If a potential data signal is returned, for example as a reflected light signal containing light and dark transitions characteristic of bar code information, then the scanner is activated, comes up to full operation and scans repetitively for a time. This test scanning method likewise consumes a good deal of battery power in determining when to switch into the active mode.
Scanning a bar code typically involves applying an illuminating beam and accumulating a response signal for a number of scanning repetitions. The reflected signal is accumulated and averaged, thereby reducing the adverse effects of some kinds of damage or dirt on a barcode label.
Power consumption and battery issues are perhaps less of an issue for a hand-held scanner that is wired to a stand or kept in a stand during scanning. The scanner may be inductively or electromagnetically coupled to a stand or base or docking station for charging. It still may be advisable to switch the device between modes of operation. For example, the scanner might be activated for scanning upon detection of its being manually removed from a charging stand. One way of generating an in-stand versus out-of-stand signal is to provide a magnet and a responsive Hall effect switch that interact when the scanner is on the charging stand. Components and circuitry are thus needed to generate an in-stand/-out-of-stand signal, which contribute to the cost of the scanner unit.
What is needed is a way to switch a scanner positively and conveniently between a power saving mode and a scanning mode without adding elements, expense or complication.